1. Field of the Invention
The present invention relates to a current sensor and a molding method thereof, and especially to a current sensor having a conductor through which a current flows, a shield plate of ring shape and a magneto-electronic conversion element and a molding method thereof. The shield plate is arranged around a flow direction of the current. The magneto-electronic conversion element detects magnetic flux density of a magnetic field which is generated when the current flows through the conductor, and converts the magnetic flux density into an electric signal.
2. Description of the Related Art
A current sensor shown in FIG. 9 is generically known as the above mentioned current sensor. (For example, see the patent documents 1-3). As shown in FIG. 9, the current sensor has a bus bar 1 as a conductor through which a current flows, a core 2 of ring shape as a shield plate and a magneto-electronic conversion element 3. The core 2 is arranged around a flow direction Y1 of a current of the bus bar 1. The magneto-electronic conversion element 3 detects magnetic flux density of a magnetic field which is generated when the current flows through the conductor, and converts into an electric signal. The magneto-electronic conversion element 3 is arranged in a gap mounted in the core 2.
When a current flows through the bus bar 1, the above mentioned current sensor generates a magnetic field of magnetic flux density according to the current thereof. The magnetic conversion element 3 converts magnetic flux density of a magnetic field which is converged by the core 2 into an electric signal, and outputs a signal according to the current. Furthermore, the core 2 shields an effect on the magnetic field from an outside.
The magnetic flux density of the magnetic field, which is generated in the gap of the core 2, peaks at the central part of the gap, and decreases quickly toward the end part of the gap. Consequently, a case and a filter (resin) are expanded and contracted depending on a surrounding temperature. When a position of the magneto-electronic conversion element 3 moves in the gap, the magnetic flux density of the magnetic conversion element 3 is changed. Thereby, an output of the magneto-electronic conversion element 3 is changed. As a result, a current can not be measured accurately.
Linearity of the current flowing into the bus bar 1 cannot be maintained so that the core 2 magnetically saturates immediately when the gap is small. For this reason, a current range which can be measured by the current sensor is narrow.
According to the above problem, heretofore, by increasing the gap area and keeping a portion which a change of magnetic flux density is equalized with, magnetic-saturation does not occur when a large current flows. In general, after a core winds annularly a zonal member configured with anisotropic silicon steel, the core is formed by cutting the gap portion. Also, the core is formed by laminating multiple plate members having a permalloy which is cut in C-shaped. As discussed previously, it is required to increase number of turns of the zonal member and laminations of the plate member so that the gap area is increased. Thereby, it causes an increase in cost.
Patent Document 1:                Japan published patent application 2006-78255        Japan published patent application 2005-308527        Japan published patent application 2001-66328        